A traditional LINAC has a mount plate with an adaptor which accepts different accessories. Almost all of these accessories are “interlocked” with coding so that the installation of the wrong accessory does not allow for radiation to be delivered to the patient. The unique code for each accessory is specified during the computer assisted creation of the patient's treatment plan.
However, problems can arise with the use of certain accessories, particularly small field circular collimators, which are typically used to treat small brain lesions. Small field circular collimators are not interlocked with coding and therefore their use may result in human error, which can lead to serious clinical mistakes. For example, the small field circular collimator may be improperly used or left off entirely, but there is no mechanism to alert the operator and/or prevent the LINAC machine from operating. The present invention solves this problem by disclosing a set of small field circular collimators which are capable of being individual identified by sensors incorporated in the adaptor of the LINAC.